Direct Observation of the Kinetics of an Atmospherically Important Reaction at the Air−Aqueous Interface

Abstract

Many atmospherically important chemical processes are believed to occur at the interface between the air and aqueous phases. We report the first direct measurement of the kinetics of a reaction between a gas-phase species (ozone) and a compound (anthracene) adsorbed at the air−water interface. The reaction was studied at the “clean” air−water interface and also at an interface consisting of approximately one monolayer of 1-octanol. In both instances, the reaction was seen to follow a Langmuir−Hinshelwood mechanism, in which ozone first adsorbs to the surface and then reacts with adsorbed anthracene. Using typical atmospheric ozone concentrations, a reactive uptake coefficient of approximately 6 × 10-8 at the air−water interface may be estimated; this value increases by about a factor of 5 when the water surface is coated by a monolayer of 1-octanol.